The AirAsia jetliner that crashed into the Java Sea with 162 people aboard stalled after climbing too fast, according to Indonesian officials who said the plane was unlikely downed by terrorism.

No sounds of gunfire or explosions were heard in cockpit voice recordings from Flight QZ8501, investigators said Tuesday, CNN reported.

The ill-fated airliner went down Dec. 28 during a flight from the Indonesian city of Surabaya to Singapore.

The pilot had asked to climb to avoid a storm but was initially denied permission because of heavy traffic in the area.

“In the final minutes, the plane climbed at a speed which was beyond normal,” Transport Minister Ignasius Jonan said, citing radar data, Agence France-Presse reported. “The plane suddenly went up at a speed above the normal limit that it was able to climb to. Then it stalled.”

He said earlier that radar data showed the Airbus A320-200 appeared to be climbing at a rate of 6,000 feet a minute before the crash.

“I think it is rare even for a fighter jet to be able to climb 6,000 feet per minute,” he said. “For a commercial flight, climbing around 1,000 to 2,000 (feet) is maybe already considered extraordinary, because it is not meant to climb that fast.”

After an initial analysis of the voice recorder, investigators said they are focusing on the possibility of human error or problems with the plane.

“We didn’t hear any other person, no explosion,” investigator Nurcahyo Utomo said in explaining why terrorism was ruled out.